1. Field of the Invention
The present claimed invention relates to the field of semiconductor wafer fabrication. More specifically, the present claimed invention relates to the alignment of wafer handling and receiving devices used in automated semiconductor wafer fabrication processes.
2. Prior Art
Many of the current semiconductor fabrication processes utilize robotic or automated semiconductor wafer handling devices. These robotic or automated devices are frequently used to convey semiconductor wafers from one position to another during the numerous fabrication or process steps used in the formation of semiconductor devices. The following is one example of the operation of a typical automated semiconductor wafer handling device found in, for example, a metal etching system such as the 8330 Precision Etch System by Applied Materials of Santa Clara, Calif. A semiconductor wafer gripper assembly is located on the distal end of extension rods, or arms, of the automated semiconductor wafer handling device. When the automated device is in a resting or "home" position, the wafer gripper assembly is proximate to a shuttle plate of a semiconductor wafer dispersing device. The semiconductor wafer dispersing device moves the shuttle plate towards a cassette of pre-processed semiconductor wafers wherein a pre-processed wafer is transferred onto the shuttle plate. The wafer dispersing device then causes the shuttle plate to return to a position proximate to the wafer gripper assembly's home position. Upon activation, the extension rods of the automated handling device extend to move the wafer gripper assembly to a position wherein the gripper assembly is able to grasp the semiconductor wafer present on the shuttle plate of the wafer dispersing device.
Next, the automated semiconductor wafer handling device changes position such that the semiconductor wafer secured in the wafer gripper assembly is moved proximate to a semiconductor wafer receiving device. Commonly, the wafer receiving device will have numerous stations, or pedestals, on which the semiconductor wafer may be placed. One type of wafer receiving device having numerous pedestals is referred to as a hexode. In a hexode, the semiconductor wafer receiving device is comprised of a six-sided columnar structure having three vertically stacked pedestals on each side. Thus, the hexode can accommodate 18 wafers at a single time. The surface of each pedestal is vertically oriented such that the semiconductor wafers are positioned "standing up", with the back surface of the wafer against the pedestal. A support button is present at the base of each pedestal, to support the semiconductor wafer.
Thus, the automated semiconductor wafer handling device must be able to place a wafer on each of the three pedestals present on each of the six sides of the hexode of the wafer receiving device. Typically, the hexode rotates so that only one side of the hexode is positioned to receive wafers from the automated wafer handling device at a time. The placement of a semiconductor wafer onto a pedestal of the wafer receiving device is repeated until each of the 18 pedestals present on the hexode is filled.
After the wafers present on the hexode have been processed, one side at a time of the hexode is presented to the handling device for removal of the processed wafers from the pedestals. After the automated handling device has picked up a processed wafer, the handling device returns to the home position. At the home position, the wafer gripper assembly deposits the processed wafer onto an empty shuttle plate of the wafer dispersing device. The wafer dispersing device moves the shuttle plate to a position wherein the processed wafer is inserted into a cassette used to hold processed wafers. These steps are also repeated until all the processed wafers have been removed from the pedestal and placed into the cassette.
In order to effectively and safely place the wafer onto the pedestal of the wafer receiving device in the correct position, several critical parameters must be met by the automated wafer handling device. When placing a semiconductor wafer onto a pedestal, the extension rods on which the wafer gripper assembly is attached must extend to exactly the right distance. If the extension rods extend too far, the wafer gripper assembly will be forced against the wafer receiving device causing damage or even breakage of the wafer. If the extension rods do not extend far enough, when the wafer gripper assembly releases the semiconductor wafer, the wafer will not be placed on the pedestal. In such a case, the wafer is simply dropped and is often ruined.
In addition to controlling the extension distance of the wafer gripper assembly, the height of the gripper assembly with respect to the pedestal must also be precisely controlled. If the gripper assembly approaches the wafer receiving device at too great of a height, when the wafer is released against the vertically oriented pedestal, the back surface of the wafer will slide down the face of the pedestal until the bottom edge of the wafer contacts the support button. The sliding motion of the back surface of the wafer against the pedestal will generate contaminate particles, and will also result in damage to the wafer. On the other hand, if the wafer approaches the pedestal at too low of a height, the bottom edge of the wafer will not be supported by the support button and the wafer will be dropped and ruined. Additionally, if the wafer approaches the pedestal at too low of a height, the back surface of the wafer may be forced against the support button located at the base of the pedestal and the wafer may be damaged or broken.
Furthermore, the wafer must be centered with respect to the pedestal. That is, when the wafer gripper assembly releases the wafer onto the pedestal, the center of the back surface of the wafer should be located directly over the center of the pedestal. This is done to insure that the wafer is resting securely against the pedestal.
Additionally, the automated wafer handling device must also be precisely aligned to insure that parallelism exists between the wafer assembly and the pedestal. That is, the automated wafer handling device must be aligned with the wafer receiving device such that when the wafer is presented to the pedestal by the wafer gripper assembly, the back surface of the semiconductor wafer is parallel to the surface of the pedestal. During fabrication of the semiconductor wafer, it may be necessary to apply an electrical bias to the wafer. The application of such an electrical bias is frequently done through the pedestal. That is, the surface of the pedestal is used to electrically bias the semiconductor wafer. In order to insure thorough contact between the semiconductor wafer and the pedestal, parallelism between the wafer and the pedestal must be achieved. Therefore, the automated wafer handling device must be aligned with the wafer receiving device such that the wafer gripper places the wafer onto the pedestal with the back surface of the wafer flush against the pedestal.
In an attempt to attain proper alignment between the automated wafer handling device and the wafer receiving device, alignment tools are often used. Many of the prior art alignment tools are comprised of a bulky elongated connecting pieces which are used to physically connect the automated wafer handling device to the wafer receiving device. These tools frequently require a substantial set-up time, involve complicated attachment procedures, and are extremely costly. Typically, one end of the alignment tool is attached to the base of the automated wafer handling device, and another end is attached to a pedestal of the wafer receiving device. The attachment of the tool to the pedestal is often performed using screws or other attachment devices. Therefore, in order to check the alignment of the wafer handling device with each of the pedestals on a wafer receiving device such as a hexode, the alignment tool must be attached to and detached from the hexode numerous times. Thus, the repeated attachment and detachment of the alignment tool to the wafer receiving device results in a lengthy set-up time to perform the alignment procedures using prior art alignment tools.
In addition to requiring substantial connections, many of the prior art alignment tools also require considerable disassembly of the automated wafer handling device. That is, in order to perform the alignment procedures, the wafer handling device must have several parts removed therefrom to accommodate the attachment of the bulky alignment tool to the wafer handling device.
In addition to the bulky prior art base alignment tool, a separate extension rod alignment tool is often attached to the extension rods of the automated wafer handling device. The position of the extension rod alignment tool is compared to the position of the base alignment tool. The position of the automated wafer handling device and the wafer receiving device is then adjusted according to the relative position of the two tools.
More specifically, the user programs stepper motors which control the motion of the automated wafer handling device. The user programs the stepper motors such that the motors cause the wafer handling device to move such that the alignment tool is positioned as desired with respect to the base alignment tool. The user may program the stepper motor such that the motor extends the extension arms, for example, 5 steps. The user then visually inspects the relative position of the base alignment and extension rod alignment tool. If the user believes that the extension rod tool has been inserted too far, the user may program the stepper motor to extend, for example 4 steps. The process is repeated until the user feels that the proper positioning and alignment of the two tools has been achieved. In so doing, it is intended that when the wafer gripper assembly is placed on the extension rods, the automated wafer handling device will position and align the gripper assembly as desired with respect to the pedestals of the wafer receiving device.
However, the comparison of the base alignment and the extension rod alignment tool and the programming of the stepper motors is based upon the visual observations of the user. Thus, different users may program the stepper motors differently. Therefore, the alignment tools of the prior art do not provide for uniformity of use among separate users.
Thus, the need has arisen for an inexpensive tool to align an automated wafer handling device with a wafer receiving device without requiring extensive disassembly of the wafer handling device, substantial set-up time, complicated attachment procedures, and which provides for uniformity of readings even when operated by separate users.